Hi,
1. To insert the image before the text, insert the next code into Customizing->General->Additional CSS:
.payment_method_paypal label:before{
display: inline-block;
margin:15px;
width:74px;
height: 46px;
vertical-align:bottom;
content: "";
background: url(https://www.paypalobjects.com/webstatic/mktg/logo/pp_cc_mark_74x46.jpg) no-repeat 0 0;
background-size: 100%;
}
2. To substitute the text with the image insert the next code instead of the previous code:
.payment_method_paypal label{
color:transparent;
}
.payment_method_paypal label:before{
display: inline-block;
margin:15px;
width:74px;
height: 46px;
vertical-align:bottom;
content: "";
background: url(https://www.paypalobjects.com/webstatic/mktg/logo/pp_cc_mark_74x46.jpg) no-repeat 0 0;
background-size: 100%;
}
Regards